The invention relates to a method for filling large-volume gas containers, especially airships, with a process gas, as well as a method for purifying the process gas contained in such a gas container, and a method for emptying such gas containers.
In recent years, the forgotten field of airship navigation has regained some of its former popularity. Airships filled above all with helium have been proposed for a multitude of possible applications, especially for transporting heavy loads. Naturally, airships of this kind must first be filled with the gas required to lift them, for example, helium. In this patent application, the gas used to fill the gas container will be referred to as process gas. After a certain period of operation, contaminants will appear in the process gas inside the airship, which effect a reduction in uplift. For example, a contamination of the helium filling with a 5% fraction of air corresponds to a 5% reduction in uplift with respect to a filling that contains nearly 100% pure helium. For this reason, the process gas filling in the airship must be periodically purified. Ultimately, the airship will also have to be emptied, for example, for maintenance. For small and medium-sized airships with up to approx. 6,000 m3 gas holding capacity, the filling or refilling is ordinarily implemented from gas cylinder transport vehicles, so-called cylinder trailers. For larger airships with a gas holding capacity of more than 6,000 m3 (for example, 400,000 m3) it has thus far been impossible to supply this quantity of gas within a short enough period of time. Excessively long down times for filling, purifying, and refilling of the airship could hamper the cost effectiveness of this type of transportation system.
It is thus the object of this invention to provide a method of filling, purifying, and emptying gas containers, via which even very large gas containers can be filled, purified, and emptied within a cost-effective period of time.
This object is attained in terms of the filling of the gas container, in that the gas container is first filled with an auxiliary gas, which possesses a higher or lower density than the process gas. The process gas to be used for the actual filling of the container is then introduced in such a way that no significant mixing with the auxiliary gas occurs, wherein, if the density of the process gas is lower than that of the auxiliary gas, the process gas is introduced into the upper area of the gas container while at the same time the auxiliary gas, or a mixture of auxiliary gas and process gas, is removed via suction from the lower area of the gas container. In contrast, if the density of the process gas is higher than that of the auxiliary gas, the process gas is introduced into the lower area of the gas container, and the auxiliary gas, or a mixture of auxiliary gas and process gas, is simultaneously removed via suction from the upper area of the container.
As was mentioned above in the introduction to the description, in this patent application, the gas that is actually used to fill the gas container will be referred to as process gas. Especially for the use in airships, a gas or gas mixture that has a lower density than air, preferably helium, hydrogen, or a mixture of helium-hydrogen is used as process gas.
The auxiliary gas, which serves only to support the filling or emptying process, is to be differentiated from this process gas. Basically, the auxiliary gas that is used possesses a higher or lower density than the process gas, with the difference in densities between the auxiliary gas and the process gas preferably amounting to at least 15%. Especially when filling and emptying airships, a gas or gas mixture having a density that is the same as or higher than air is used as the auxiliary gas. In the simplest case, the auxiliary gas is comprised of air. Expediently, the gas container is completely filled with the auxiliary gas before the process gas is introduced.
Under a quiescent introduction of the process gas it is to be understood that, to the greatest possible extent, no or very slight turbulent gas streams are produced in the gas container, which would cause the process gas being introduced to mix with the gas already present in the gas container. The flow rate, the inflow cross section, and the point of introduction are selected purposely so that a turbulence of the introduced process gas can be excluded. Only the quantity of auxiliary gas that is drawn, for example, from the lower area of the gas container is replaced with the process gas that is introduced, for example, in the upper area of the gas container.
The exchange of gases is preferably implemented as quickly as possible, in order to keep the diffusion of the two media at an insignificant level. Expediently, the exchange of gases takes less than 20 hours.
When the process gas is introduced into the gas container, a mixing zone forms as a result of physical effects (for example, diffusion, convection), in which the process gas and the auxiliary gas become mixed with a concentration drop within the mixing zone. In the case wherein the density of the process gas is lower than that of the auxiliary gas, this mixing zone travels downward as the filling process advances, until the mixing zone ultimately reaches the bottom of the gas container. In the reverse case, the mixing zone travels upward. The process gas/auxiliary gas mixture can be fed to a purification device when it has reached a minimum process gas concentration of 50%.
Because the thermal effects can influence the mixing of the process gas and auxiliary gas, differences in temperature between the process gas and the auxiliary gas should be taken into account. Differences in temperature can be either avoided to exclude additional influences, or intentionally introduced to generate differences in density based upon temperature differences between the process gas and the auxiliary gas.
After the fill process has been completed and the operation of the gas container has begun, a contamination of the helium may develop over time, for example, as a result of the diffusion of air through the walls of the container. In order to purify the process gas in the gas container, purified or fresh process gas that has a higher level of purity than the process gas already contained in the gas container is quiescently introduced into the gas container in such a way that no significant mixing with the contaminated process gas in the container occurs. In this process, if the contamination of the process gas has resulted in an increase in the density of the process gas, then the purified or fresh process gas is introduced into the upper area of the gas container, while at the same time the contaminated process gas is removed via suction from the lower area of the gas container. Inversely, in the case wherein a contamination of the process gas has resulted in a decrease in the density of the process gas, then the purified or fresh process gas is introduced into the lower area of the gas container, while at the same time contaminated process gas is removed via suction from the upper area of the gas container.
Finally, to empty a gas container filled with process gas, the process gas is extracted by suction from the gas container, while auxiliary gas having a lower or higher density than the process gas is quiescently introduced into the gas container in such a way that no significant mixing with the process gas occurs.
In this, if the density of the process gas is lower than that of the auxiliary gas, the process gas is removed by suction from the upper area of the gas container, while the auxiliary gas is simultaneously introduced into the lower area of the gas container. Inversely, if the density of the process gas is higher than that of the auxiliary gas, the process gas is removed by suction from the lower area of the gas container, while the auxiliary gas is simultaneously introduced into the upper area of the gas container.
To enable the quiescent introduction of the process gas into the gas container, it is preferably introduced over the cross section of the gas container or distributed at the upper and lower walls at a low flow rate. To this end, for example, so-called plate aerators or perforated tubes are provided, which extend over a majority of the gas container cross section or along the length of the gas container. The gas inlet device, which is configured expediently round or flat, is preferably positioned inside the container at the highest or lowest point of the gas container. However, gas inlet devices that are not flat are also conceivable. Accordingly, during emptying of the gas container, the auxiliary gas is also preferably distributed over the cross section of the gas container, and is introduced at a low flow rate. Similarly, during removal of the process gas it is ensured that no turbulence of the process gas takes place inside the container.
The invention is provided especially for use in very large gas containers, for example, airships, having a gas volume of more than 6,000 m3, preferably more than 50,000, especially 50,000 to 2,000,000 m3 (for example, 400,000 m3). During the filling of this type of gas container, the process gas is preferably introduced into the gas container over approx. 10 to 100 hours at a volumetric flow rate of at least 500 m3n/h. During the purification of the process gas inside the gas container, the purified process gas is advantageously piped into the gas container and contaminated process gas is removed by suction at a volumetric flow rate of at least 500 m3n/h.
Because with very large gas containers having gas filling capacities of, for example, 400,000 m3 the quantity of gas needed to fill the container cannot be provided directly via gas transport vehicles, for example, cylinder trailers, a further development of the concept of the invention envisions the process gas being intermediately stored in pressurized gas tanks, which can be filled gradually from the gas transport vehicles. In this manner, gas transport vehicles can supply the process gas, which is compressed via high-pressure compressors to, for example, 80 bar and is stored in the pressurized gas tanks, over a longer period of time. As a result, the quantity of gas needed to fill the gas container is available at any time. In this manner, even large-volume gas containers can be filled with large quantities of process gas within the shortest possible time.
When purifying the process gas in the gas container, at least two pressurized gas tanks are preferably used, at least one of which is filled with contaminated process gas from the gas container, while at least one other pressurized gas tank supplies the purified process gas to fill the gas container. In this, the contaminated process gas that is intermediately stored in the pressurized gas tank is expediently purified using a membrane purification device, and is intermediately stored as purified process gas in the pressurized gas tank. The process gas can also be purified, for example, by adsorption or rectification processes.
Overall, by using pressurized gas tanks, the time required to fill, purify, and empty large-volume gas containers, especially airships, is minimized. As a result, the down times needed by the airships can be limited to an economically acceptable duration.
The proposed method is suitable for use with all types of gases. The use in airships, the use of helium or hydrogen or a helium-hydrogen mixture is especially envisioned. The invention can, however, also be used, for example, for balloons filled with hydrogen or for large-capacity tanks, gasometers, etc. filled with helium, hydrogen, or other gases. When used in large-capacity tanks and gasometers, nitrogen is preferably used as the auxiliary gas in place of the otherwise preferred air.
The invention offers a number of advantages. For example, with the process specified in the invention, the gas container, specifically the airship, always remains tightly filled, so that changes in tension in the hull of the gas container are minimized. The principal advantage of the invention, however, consists in that the filling, purification, and emptying of the gas container can be implemented very rapidly. Thus, the cost efficiency of this system of transportation is made possible with large-volume airships, since the necessary down times can be minimized.